This invention is related to a ceramic dielectric waveguide filter of the type in which a plurality of resonators are spaced longitudinally along the length of a monoblock and in which a plurality of slits are spaced longitudinally along the length of the monoblock and define a plurality of bridges of ceramic dielectric material between the plurality of resonators.
Experiments have demonstrated that waveguide filters can be accurately modeled using commercially available 3D electromagnetic simulators.
Experiments have also demonstrated that the frequency response curves of an actual prototype waveguide filter nearly matches the modeled waveguide filter but that the center frequency does not match because the absence of accurate information regarding the relative permittivity of the dielectric material of the waveguide filter makes it very difficult to match the center frequency of the actual part to the center frequency of the modeled waveguide filter.
Fortunately, however, within a batch of prototype waveguide filters, the relative permittivity does not vary significantly so that all of the parts made from the same batch of material can be expected to have nearly identical center frequencies assuming reasonable reproduction of dimensions. Tools used to make these waveguide filters are quite expensive which makes it impractical to adjust the tool to match the material properties.
In the case of combline filters of the type disclosed in U.S. Pat. No. 4,800,348 to Rosar et al., it has been standard practice to adjust the center frequency of the filter by tuning individual resonators of the finished filter. This process is time consuming and labor intensive. In the past, bulk tuning was implemented for certain combline filters that were designed without any thick film conductor pattern. However, the majority of combline filters in use today are manufactured with a conductor top print which prevents successful implementation of bulk tuning.
Unlike combline filters, however, there is no simple way of probing individual resonators in a finished waveguide filter, and thus it is very difficult to adjust the filter center frequency by tuning individual resonators. The present invention is directed to a waveguide filter which has been tuned by adjusting the width of the waveguide filter.